Transcript Star Formation and Protostars at High Angular Resolution with the

Star Formation and Protostars at High
Angular Resolution with the SMA
Jes Jørgensen (CfA)
Tyler Bourke, Philip Myers, David Wilner (CfA),
Fredrik Schöier (Stockholm), Ewine van Dishoeck (Leiden),
... and the PROSAC team.
ACP
Submillimeter Astronomy in the era of the SMA, Cambridge, June 14, 2005
Dark Cloud Cores
t ~ 105 – 106 yrs
T-Tauri star, disk,
outflow
t=0
Gravitational
collapse
t ~ 106 – 107 yrs
t ~ 104 – 105 yrs
t > 107 yrs
Protostar
embedded in
~10,000 AU
envelope
Main-sequence star,
planetary system
Pre-main
sequence star,
remnant disk
Figure based on Shu (1987); from “NASA Origins”
Low-mass protostars
~ 20,000 AU (100”)
~ 200 AU (1”)
• Densities ranging from 104 cm-3 to 107-108 cm-3 (H2)
• Temperatures ranging from ~10 K to a few hundred K.
PROSAC
PROtostellar Submillimeter Array Campaign
Jørgensen (PI)
Bourke, Di Francesco, Lee, Myers, Ohashi,
Schöier, Takakuwa, van Dishoeck, Wilner, Zhang
 Line + continuum survey (230/345 GHz) of deeply embedded (class 0)
protostars
 8 protostellar sources from Ph.D. thesis of J. Jørgensen (Leiden
Univ. 2004; Jørgensen et al. 2002, 2004, 2005)...
 Single-dish survey at JCMT and Onsala 20m telescopes.
 Follow-up 1, 3 mm interferometric measurements OVRO and BIMA.
 All tied together by detailed line and continuum rad. transfer models.
 3 spectral setups per source: CO, CS, SO, HCO+, H2CO, CH3OH,
SiO, ... transitions (and isotopes)
In this talk...
 What is the structure of protostellar envelopes on a few 100 AU
scales?
 What is the physical structure of circumstellar disks - and their
molecular content?
 Do low-mass protostars have hot cores, i.e., inner regions with
temperatures higher than 100 K and where complex organic
molecules might be present?
NGC1333-IRAS2
SCUBA 850 µm
2A
2C
Tbol ~ 50 K, Lbol ~ 16 L
d ~ 220 pc (Cernis, 1990)
2B
Three pre/protostellar objects
(Looney et al. 2000, Sandell & Knee 2001,
Jørgensen et al. 2004)
NGC1333-IRAS2A dust continuum at 850 µm.
SCUBA 850 µm
SMA 850 µm
NGC1333-IRAS2A dust continuum at 850 µm.
…the SMA resolves the warm dust in the inner envelope
and the circumstellar disk
SMA 850 µm
Envelope (constrained through SCUBA
observations; Jørgensen et al. (2002))
Disk (resolved)
NGC1333-IRAS2A dust continuum at 850 µm.
 The dust continuum emission
follows a power-law F   2.2
from cm through submillimeter
wavelengths.
 Likely optically thick thermal
dust emission from a
circumstellar disk with a size of
300 AU and mass of
a few  0.01-0.1 M
 It is not evident from highresolution data that the
envelope extends all the way to
the smallest scales.
 The disk material will be
dominating a hot core in the
protostellar envelope.
cm through mm measurements from Rodríguez et al. (1999), Reipurth et al. (2002), Jørgensen et al. (2004)
Envelope and disk chemistry
 Low-mass hot cores: Presence of complex organic species on small
scales (i.p., IRAS16293: Cazaux et al. (2003), Kuan et al. (2004),
Bottinelli et al. (2004)).
Detections of high excitation
transitions of CO, HCN (and
H13CN), SO, SO2, CH3OH (and
CH3OD), CH3OCH3 and
CH3OCHO (tentative) in
submm window toward
NGC1333-IRAS2A.
Organic molecules toward IRAS2A
500 AU
...line emission compact (largely unresolved)
Envelope and disk chemistry
 Low-mass hot cores: Presence of complex organic species on small
scales (i.p., IRAS16293: Cazaux et al. (2003), Kuan et al. (2004),
Bottinelli et al. (2004)).
 Complex organic species detected on small scales in IRAS2A.
 ...but in the 2” SMA beam: the disk column density is dominating
compared to the hot core.
 Sulfur species are expected to be enhanced in typical hot cores
(Charnley 1997, Wakelam et al. 2004)
Envelope and disk chemistry
With SO abundance
enhancements in hot core
Constant abund. envelope
The SO abundance is almost
constant throughout the
envelope (consistent with
single-dish obs. of S-species).
An abundance enhancement in
the innermost envelope is
clearly ruled out.
Envelope and disk chemistry
 Low-mass hot cores: Presence of complex organic species on small
scales (i.p., IRAS16293: Cazaux et al. (2003), Kuan et al. (2004),
Bottinelli et al. (2004)).
 Complex organic species detected on small scales in IRAS2A.
 ...but in the 2” SMA beam: the disk column density is dominating
compared to the hot core.
 Sulfur species are expected to be enhanced in typical hot cores
(Charnley 1997, Wakelam et al. 2004)
 The presence of the high excitation lines of in particular CH3OH
suggests that the temperature is high ~ 150 K. Heated layer of
circumstellar disk (e.g., Elias 29; Ceccarelli et al. 2002)?
Jørgensen et al., ApJ, submitted
...much more to come!
Conclusions
 High-angular resolution interferometric and single-dish
continuum observations of NGC 1333-IRAS2A can be fitted by
an extended envelope and a 300 AU (resolved) disk with a mass
a few  0.01-0.1 M.
 The large size of the disk suggests a rapid build-up of disks in
the deeply embedded stages of protostellar evolution.
 The molecular content of the disk is non-negligible compared to
a candidate hot core. It is not evident from the dust
observations/models that warm (T > 100 K) material is present
in the envelope around NGC1333-IRAS2A.
 No evidence is seen for sulfur enhancements on small-scales.
Other species such as CH3OH may have their origin in the
circumstellar disk... (don’t forget the outflows, though)